The behavioral, biochemical, and histological effects of tissues implanted into the brain of mammals is being studied. Rodent and primate models of Parkinson's disease are recipients for dopaminergic tissue implants. Fetal mesencephalic grafts to the striatum have been the most successful for restoration of function in the primates. We have also observed sprouting from non- damaged dopaminergic cells in the implanted animals. This may be the basis of the functional recovery and is now under active investigation. Part of our effort has been to perfect the technical aspects of stereotactic implantation of dispersed cells into brain. We identified the factors which influence the accuracy of cell placement, and will now use this information to implant various dopaminergic cells into the brains of lesioned animals. In addition, we are developing a model of intracerebral pancreatic islet implantation in diabetic rats to facilitate studies of interaction of the peripheral immune system and tissue grafts into the brain.